1. Field of the Invention
The present invention relates to a runflat tire system which allows a vehicle to run safely at a constant speed through a predetermined distance even when an internal pressure of a tire is lowered.
2. Description of the Related Art
In recent years, a runflat tire system by which, even if the tire goes flat, it is possible to travel for a very long distance for example several hundred kilometers at a relatively high speed of up to about 80 km/hr has been proposed.
FIG. 8 shows a conventional system of this kind. The system comprises a tire “a”, a wheel rim b on which the tire “a” is mounted, and a support ring e mounted on the wheel rim b in a cavity i surrounded by the tire “a” and the wheel rim b. When an internal pressure of the tire is reduced, the support ring e contacts against an inner surface of a tread portion d to support a load of the tire. The wheel rim b comprises first and second seats b1 and b2 on which first and second bead portions f1 and f2 of the tire “a” are mounted. A mounting part g for the support ring e is provided between the seats b1 and b2.
In this system, as shown in FIG. 9, when the internal pressure of the tire “a” is reduced due to puncture or the like, the inner surface d1 of the tread portion d contacts against the support ring e. A load applied to the tire “a” is supported by the support ring e and the wheel rim b. Since the first bead portion f1 and the second bead portion f2 are locked between a rim flange and a hump h, the vehicle can run at such speed that no problem is caused in a runflat manner. This system eliminates a need for exchanging tires on a road shoulder, and allows the vehicle to move to a gas station or a service garage. Thus, it is desired that the runflat tires become widespread in terms of safety at the time of high speed running in addition to convenience and comfort.
As noises generated by a tire, there is a road noise. The road noise is generated if air resonates in the cavity i when a vehicle runs on a rough road, and the road noise causes a roaring sound in a frequency range of about 50 to 400 Hz. The road noise is transmitted into a passenger room and becomes a muffled sound, and this offends a passenger in the vehicle.
Like general tires, it is important to reduce the road noise for improving habitability also in the runflat tire system.
Conventionally, Japanese Patent No. 3373596 proposes a runflat system as shown in FIG. 10 in which a tire resonance preventing member q made of porous material or fiber material is disposed around an outer surface of a core body p having substantially T-shaped cross section. This technique is intended for the reduction of cavity resonance having main frequency of around 250 Hz at which the resonance becomes a noise.
As shown in FIGS. 11 and 12, Japanese Patent Application publication No. 2003-502200 (WO 00/76791 A1) proposes a runflat system in which an annular supporting body r mounted on a rim forms a resonator comprising a large number of cavities u defined by supporting wall portions w3 between an outer peripheral wall w1 and an inner peripheral wall w2, and a sidewall w4 closes the resonator. The sidewall 4 is provided with tubes v which are in communication with the cavities. In this proposal, vibration characteristics of the resonator is optimized by the tubes v based on the principle of the Helmholtz resonator, thereby suppressing the resonance.
According to the former system, however, the tire resonance preventing member q mounted on the surface of the core body p comes into contact with a surface of the cavity at the time of runflat running. Thus, the friction heat at the time of runflat running is reduced and lubricant which was previously applied to the cavity surface is absorbed or wiped off by the tire resonance preventing member q, and there is a problem that the runflat endurance is deteriorated. Further, the core body p having substantially T-shaped cross section is heavy and deteriorates the rolling resistance.
The latter system also has a problem that since the sidewall w4 is heavy, the entire weight is increased. Further, this system requires complicated and severe operations such as mounting operation of the tubes v on the sidewall w4, mounting operation of the cavities on the sidewall w4, and tuning operation of the vibration characteristics of the resonator, so that it takes a lot of trouble to assemble.
It is a main object of the present invention to provide a runflat tire system which reduces road noise by suppressing the resonance in the cavity, and which is light in weight and has excellent runflat endurance, and to provide a support ring used for the runflat tire system.
According to the present invention, a runflat tire system comprises:
a pneumatic tire;
a wheel rim on which the pneumatic tire is mounted; and
a support ring made of elastic material and disposed in a cavity surrounded by an inner surface of the rim and an inner surface of the tire mounted thereon, wherein
the support ring comprises an annular body extending in a circumferential direction of the tire and provided with a plurality of hollows opening at the cavity, and
at least one noise damper made of sponge material having apparent density of 0.1 g/cm3 or less and disposed in the hollow such that the noise damper does not protrude into the cavity from an inlet surface of the hollow.
According to the runflat tire system and the support ring used therefor of the present invention, the noise damper absorbs resonance energy in the cavity, and reduces road noise. With this, comfortable habitability in a passenger room can be obtained. Further, since the noise damper is disposed such that it does not protrude into the cavity from the inlet surface of the hollow, lubricant which was previously applied to the cavity is not absorbed or wiped off. Therefore, the runflat endurance is not deteriorated. Further, since the noise damper has low density and is light in weight, the entire system is reduced in weight.